Electrodeposition paint forms coating film excelling in performances such as corrosion resistance, finished appearance and so on, and hence is broadly adopted in the field of utility wherein such performances are required, e.g., for coating automobile bodies or their parts.
Heretofore rust-preventive agent such as lead compound or chromium compound has been blended with electrodeposition paint for further improving the latter's corrosion resistance, but these compounds are highly harmful and their use gives rise to a problem for antipollution measure. Hence investigations have been made on non-toxic or low toxic rust-preventive agent to replace these lead compound or chromium compound.
For example, JP Hei 5(1993)-65439A (=EP-A-0509437) discloses an electrocoating composition comprising dialkyltin aromatic carboxylate and bismuth compound or zirconium compound, and JP 2000-290542A discloses an electrocoating composition comprising a compound selected from the group consisting of bismuth silicate, bismuth silicomolybdate, bismuth hydroxide and zirconium compound. However, these electrocoating compositions are not fully satisfactory in respect of corrosion resistance, in particular, long-term corrosion resistance as tested by anti-weathering test.
Furthermore, JP 2004-269595A discloses a cationic electrodeposition paint of which etch pitting resistance is improved by bismuth oxide of the maximum particle size of 1.5 μm contained therein.